This article is slightly liberally biased.
What is the main function the United States Navy currently performs?
If you say “strategic deterrence to prevent Russian or Chinese aggression” or “supporting the US military in the Middle East” or something like that, you’re not completely wrong, but those functions aren’t the whole of the day in, day out bread and butter of US naval action.
One of the US Navy’s most important functions, on a day to day basis, is piracy suppression.
As an American, you can buy smartphones made in China and electronics from Taiwan and cars from Japan because the US Navy prevents piracy and allows easy, cheap, and safe trade of goods.
The US Navy is the most effective piracy suppression force on the planet. It occupies a considerable amount of naval time and resources. And because it’s the US Navy, those resources can be spent in places that most protect US commercial interests.
An isolationist United States would leave piracy suppression to others. At best, that would mean those other nations would prioritize their own commercial interests, not US commercial interests; at worst, it wouldn’t happen at all.
An isolationist United States is a really dumb idea. It would harm US commercial interests and therefore the US economy. And that’s only one of many reasons it’s a dumb idea.